CN108259711B - Image capturing device and rapid focusing method thereof - Google Patents
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- CN108259711B CN108259711B CN201611234234.8A CN201611234234A CN108259711B CN 108259711 B CN108259711 B CN 108259711B CN 201611234234 A CN201611234234 A CN 201611234234A CN 108259711 B CN108259711 B CN 108259711B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/60—Control of cameras or camera modules
- H04N23/67—Focus control based on electronic image sensor signals
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Abstract
The invention provides an image capturing device and a rapid focusing method thereof. The image capturing device comprises a lens, an image sensor, a lens control circuit and a focusing circuit. The fast focusing method includes controlling the lens to move by the lens control circuit to shoot image by the image sensor, and calculating the first and second curves of the focusing value of the shot image in the first and second scales relative to the moving steps of the lens by the focusing circuit. Then, the focusing circuit divides the focusing values of the first curve and the second curve to obtain a characteristic curve, and estimates the position of the trough according to the positions of the peak and the saddle point appearing in the characteristic curve. And finally, the lens control circuit controls the lens to move to the number of moving steps corresponding to the wave trough and then to the number of moving steps corresponding to the wave crest of the first curve or the second curve so as to finish focusing. The image capturing device and the rapid focusing method thereof can improve the focusing speed and can avoid the influence on the shooting experience of a user due to the image change caused by the back-and-forth movement of the lens.
Description
Technical Field
The present invention relates to an image capturing apparatus and method, and more particularly, to an image capturing apparatus and a fast focusing method thereof.
Background
With the increasing progress of image capturing technology, the pixels of digital cameras have been greatly increased, but the size of cameras has been relatively reduced, and the digital cameras can be configured on portable electronic devices such as mobile phones and tablet computers, so that users can capture images anytime and anywhere. In order to facilitate a user to quickly capture a clear image, a camera of a portable electronic device is generally equipped with an Auto Focus (AF) function, which can actively detect an object in a field of view of the camera and automatically move a lens to Focus on the object while the user activates the camera. Therefore, the time spent on manual focusing by a user can be saved.
Generally, in a conventional Focusing method, the optimal Focusing position is determined by using the Contrast Based Auto Focusing (CBAF) of an image, and the image Contrast is calculated in many ways, including Tenengrad function, wavelet (wavelet), Gaussian derivative (Gaussian derivative), laplace transform (laplacian transform), Finite Impulse Response (FIR) filter, Infinite Impulse Response (IIR) filter, etc., which are widely used, and the image Contrast is calculated in the form of FIR/IIR as a basis for finding the optimal Focusing position.
However, in any image contrast calculation method, the calculated image contrast value cannot sufficiently reflect the image definition due to the limitation of the reference area. At this time, the multi-scale image contrast values can be used to assist image focusing, i.e., for images of different scales, the same or different filters are applied to extract the contrast values of the images of different scales, so as to facilitate the subsequent focusing module to quickly find the best focusing position.
In general, a hill-climbing mechanism is mostly applied to a focusing strategy, and the hill-climbing strategy is determined according to the change of an image contrast value at different focusing distances (positions). Fig. 1 is a schematic diagram of a conventional camera focusing hill-climbing mechanism, which can be divided into three sections: the first stage is to apply a large step crossing manner to quickly reach the position under the mountain foot (at this time, the image contrast value at the adjacent focusing position is slightly changed); the second phase is a middle step hill climbing (the image contrast value is continuously increased, which means that the focusing position is closer to the optimal focusing distance); the third segment is after crossing the peak (at this time, the image contrast value suddenly decreases, ending the original rising trend, which indicates that the focusing position has passed the peak and surpassed the optimal focusing position), and at this time, the third segment needs to move back in small steps to move to the peak and finally reach the optimal focusing position.
The conventional mountain climbing mechanism cannot avoid the three-stage process, so that the focusing time cannot be effectively reduced, and in the process of gradually returning to the top of a mountain beyond the top of the mountain, the image is blurred, clear, fuzzy and clear, so that a user has poor shooting experience.
Disclosure of Invention
The invention provides image capturing equipment and a rapid focusing method thereof, which can accelerate the focusing speed of a camera and provide good shooting experience for users.
The invention discloses a quick focusing method of image capturing equipment, wherein the image capturing equipment comprises a lens, an image sensor, a lens control circuit and a focusing circuit. The method controls the lens to move by the lens control circuit so as to shoot the image. Then, a first curve of the focusing value of the image shot by the image sensor relative to the moving steps of the lens under the first scale and a second curve of the focusing value relative to the moving steps of the lens under the second scale are calculated by the focusing circuit. Then, the focusing circuit divides the focusing values of the first curve and the second curve to obtain a characteristic curve, and estimates the position of the trough according to the positions of the peak and the saddle point appearing in the characteristic curve. And finally, the lens control circuit controls the lens to move to the number of moving steps corresponding to the wave trough and then to the number of moving steps corresponding to the wave crest of the first curve or the second curve so as to finish focusing.
In an embodiment of the present invention, the step of calculating, by the focusing circuit, a first curve of the focusing value of the image captured by the image sensor at the first scale relative to the moving steps of the lens includes calculating, by an image contrast algorithm, contrast values of a plurality of pixels in the image at the first scale, and calculating a sum of powers of the contrast values of the pixels in the image located in the focusing frame as the focusing value of the image at the first scale.
In an embodiment of the invention, the step of calculating, by the focusing circuit, a second curve of the focusing value of the image captured by the image sensor at the second scale relative to the moving steps of the lens includes calculating, by an image contrast algorithm, contrast values of a plurality of pixels in the image at the second scale, and calculating a sum of powers of the contrast values of the pixels in the image located in the focusing frame as the focusing value of the image at the second scale.
In an embodiment of the invention, the step of estimating the position of the trough according to the positions of the peak and the saddle point appearing in the characteristic curve includes calculating a change in a slope of the characteristic curve during the process of taking the image by moving the lens, determining that the peak of the characteristic curve is reached when the slope is changed to zero, determining that the saddle point of the characteristic curve is reached when the slope is changed from zero to a maximum value, and calculating a distance between the peak and a moving step number corresponding to the saddle point, so that the moving step number corresponding to the saddle point is added with the distance forward to estimate the position of the trough.
In an embodiment of the invention, the step of controlling the lens to move to the moving steps corresponding to the trough and then to the moving steps corresponding to the peak of the first curve or the second curve by the lens control circuit to complete focusing includes controlling the lens to move to the moving steps corresponding to the trough at a first speed by the lens control circuit, and controlling the lens to move to the moving steps corresponding to the peak of the first curve or the second curve at a second speed by the lens control circuit, where the second speed is less than the first speed.
The invention provides an image capturing device, which comprises a lens, an image sensor, a lens control circuit and a focusing circuit. The image sensor is coupled to the lens for capturing an image. The lens control circuit is coupled to the lens for controlling the lens to move to capture an image. The focusing circuit is coupled with the image sensor and the lens control circuit and used for calculating a first curve of a focusing value of an image shot by the image sensor relative to the moving steps of the lens and a second curve of the focusing value of the image shot by the image sensor relative to the moving steps of the lens under a second scale, dividing the focusing value of the first curve and the focusing value of the second curve by the focusing value of the first curve and the focusing value of the second curve to obtain a characteristic curve, and estimating the position of a trough according to the positions of a peak and a saddle point appearing in the characteristic curve. The lens control circuit controls the lens to move to the number of moving steps corresponding to the wave trough estimated by the focusing circuit and then to the number of moving steps corresponding to the wave crest of the first curve or the second curve to finish focusing.
In an embodiment of the invention, the focusing circuit includes a plurality of pixels in the image of the first scale calculated by using an image contrast algorithm, and a sum of powers of the contrast values of the pixels in the image located in the focusing frame is calculated as a focusing value of the image at the first scale.
In an embodiment of the invention, the focusing circuit includes a plurality of pixels in the image at the second scale, and a sum of powers of the contrast values of the pixels in the image within the focusing frame is calculated as the focusing value of the image at the second scale.
In an embodiment of the invention, the focusing circuit calculates a change of a slope of the characteristic curve during the image taking process by moving the lens, wherein when the slope is changed to zero, a peak of the characteristic curve is determined to be reached, and when the slope is changed from zero to a maximum value, a saddle point of the characteristic curve is determined to be reached, a distance between the peak and a moving step number corresponding to the saddle point is calculated, and the distance is added forward by the moving step number corresponding to the saddle point to estimate the position of the trough.
In an embodiment of the present invention, the length and width of the second scale are fractions of the length and width of the first scale.
Based on the above, the image capturing apparatus and the fast focusing method thereof of the present invention obtain the characteristic curve by calculating the focusing value curve of the non-scale image and dividing the curve by the curve, observe the peak and saddle points from the characteristic curve, estimate the position of the trough at equal distances by using the distance between the peak and saddle points, thereby moving the lens to the focusing position corresponding to the trough in one step, and finally perform a small step search to complete focusing. Therefore, the focusing speed can be improved, and the phenomenon that the shooting experience of a user is influenced due to the fact that the lens moves back and forth to cause image change can be avoided.
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.
Drawings
FIG. 1 is a schematic diagram of a conventional camera focusing hill climbing mechanism;
FIG. 2 is a block diagram of an image capture device according to an embodiment of the present invention;
FIG. 3 is a flowchart illustrating a fast focusing method of an image capturing apparatus according to an embodiment of the present invention;
FIG. 4A is a graph showing the variation of the focus value of the first-scale image with the number of moving steps according to an embodiment of the present invention;
FIG. 4B is a graph showing the variation of the focus value of the second-scale image with the number of moving steps according to an embodiment of the present invention;
FIG. 4C is a graph showing the ratio of FV2 to FV1 according to the embodiment of the invention.
Description of reference numerals:
20: image capturing device
22: lens barrel
24: image sensor
26: lens control circuit
28: focusing circuit
FV1, FV 2: curve of focus value
SFV: curve of ratio of focus values
P1, P4: wave crest
P2, P5: saddle point
P3: trough of wave
S1, S2: tendency of variation of focusing value
d1, d 2: distance between two adjacent plates
S302 to S308: the invention discloses a fast focusing method of an image capturing device.
Detailed Description
The invention calculates the contrast value of the multi-scale image and converts the contrast value into a focus value, then observes the focus value and the change of the contrast value, identifies the peak and saddle points of the curve according to the change of the slope of the focus value ratio curve, and estimates the trough position of the curve in an equidistant mode, wherein the trough position is the area where the optimal focus position is located. Therefore, the change trend of the contrast value can be effectively estimated, the optimal focusing position can be indirectly estimated, and the aim of rapid focusing can be finally achieved.
FIG. 2 is a block diagram of an image capture device according to an embodiment of the invention. Referring to fig. 2, the image capturing apparatus 20 of the present embodiment is, for example, a Digital camera, a Digital Video recorder (DVC), or a camera configured on an electronic device such as a mobile phone, a tablet computer, a notebook computer, a navigation device, a driving recorder, etc., and can provide a camera function. The image capturing device 20 includes a lens 22, an image sensor 24, a lens control circuit 26 and a focusing circuit 28, and the functions thereof are as follows:
the lens 22 is formed by combining a plurality of meniscus lenses, and is driven by an actuator such as a stepping Motor or a Voice Coil Motor (VCM) to change the relative position between the lenses, thereby changing the focal length of the lens 22. The lens 22 is provided with an aperture, which is an annular opening formed by a plurality of metal blades and is opened or closed according to the aperture value, so as to control the light input of the lens 22, and a shutter, which is used to control the time for light to enter the lens 22, and the combination of the aperture and the shutter affects the exposure of the image captured by the image sensor 24.
The image sensor 24 is connected to the lens 22 or disposed in the lens 22, and a Charge Coupled Device (CCD), a Complementary Metal-Oxide Semiconductor (CMOS) Device or other types of photosensitive devices are disposed therein, so as to sense the intensity of light entering the lens 22 to generate an image.
The lens control Circuit 26 is, for example, an Integrated Circuit (IC), and is used for controlling an actuator in the lens 22 to drive the lens 22 to change the focal length thereof. In the present embodiment, the lens control circuit 26 receives the focusing information provided by the focusing circuit 28, and converts the focusing information into a progressive distance, so as to control the actuator in the lens 22 to drive the lens 22.
The focusing circuit 28, which is composed of a microprocessor, a digital signal processor, a programmable controller, an asic or the like, receives the image captured by the image sensor 24 and analyzes the contrast values of the image at different scales to estimate the optimal focusing position.
In detail, fig. 3 is a flowchart illustrating a fast focusing method of an image capturing apparatus according to an embodiment of the invention. Referring to fig. 2 and fig. 3, the method of the present embodiment is applied to the image capturing apparatus 20 shown in fig. 2, and the following steps of the fast focusing method of the present embodiment will be described in detail by combining various components of the image capturing apparatus 20 shown in fig. 2:
first, the lens 22 is controlled by the lens control circuit 26 to move to capture an image by the image sensor 24 (step S302). The image capturing apparatus 20, for example, starts a live view (live view) mode to capture an image after the user activates the image capturing function. The captured image is displayed on a display (not shown) of the image capturing device 20 in real time for viewing by the user. While capturing the image, the lens control circuit 26 controls the actuator in the lens 22 to move the lens to change the focal length of the lens 22 according to the focus position provided by the focus circuit 28, so as to provide the image sensor 24 to capture the image at different focal lengths.
Next, the focus circuit 28 calculates a first curve of the focus value of the image captured by the image sensor 24 in the first scale with respect to the moving step number of the lens 22 and a second curve of the focus value in the second scale with respect to the moving step number of the lens 22 (step S304). The length and width of the second dimension are one half, one quarter or other fractions of the length and width of the first dimension, and are not limited herein.
Specifically, the focusing circuit 28 calculates the contrast values of a plurality of pixels in the images of different scales by using an image contrast algorithm such as a Tenengrad function, a wavelet (wavelet), a Gaussian derivative (Gaussian derivative), a laplacian transform (laplacian transform), a Finite Impulse Response (FIR) filter, or an Infinite Impulse Response (IIR) filter, and calculates the focus values of the images of different scales by using the contrast values. For example, focus circuit 28 may calculate the sum of the powers (e.g., squares) of the contrast values of the pixels in the image that lie within the focus frame as the focus value of the image at that scale.
For example, assuming that the image of the first scale is an original image, and the image of the second scale is an image of the original image with a size of one fourth of the original image, the present embodiment calculates the contrast value fv1 of the image of the first scale by using a Finite Impulse Response (FIR) filter, and calculates the contrast value fv2 of the image of the second scale by using the same FIR method. Then, the SUM of the squares of the contrast values FV1 of the pixels located in the focusing frame in the first scale image is calculated as the focus value FV1 ═ SUM (FV1 × FV1) of the first scale image, and the SUM of the squares of the contrast values FV2 of the pixels located in the focusing frame in the second scale image is also calculated as the focus value FV2 ═ SUM (FV2 × FV2) of the second scale image.
Then, the focus value of the first curve and the second curve is divided by the focus circuit 28 to obtain a characteristic curve, and the position of the trough is estimated according to the positions of the peak and the saddle point appearing in the characteristic curve (step S306). In particular, it can be seen from a plurality of characteristic curves that the best focus position region shows a trend similar to a cubic curve, the valley of the characteristic curve is also in the best focus position region, and the peak of the characteristic curve is generally located at the saddle part of the first curve or the second curve.
Accordingly, when the focusing circuit 28 uses the first curve or the second curve as the basis for climbing (i.e. moving the lens 22 to gradually increase the contrast value or the focus value of the image captured by the image sensor 24), the change of the characteristic curve is observed in addition to the change of the first curve and the second curve during the climbing process. When the peak of the first curve or the second curve is reached, the peak is approximately near the peak of the characteristic curve. The first curve, the second curve, and the change in slope of the characteristic curve may be monitored simultaneously as the peak of the characteristic curve is crossed (i.e., the slope of the characteristic curve transitions from a negative value to a positive value or from a positive value to a negative value). When the slope of the characteristic curve reaches the maximum value (which may be a negative value or a positive value) of the region, it can be determined that the current focusing position reaches the saddle point of the characteristic curve.
Based on the symmetrical characteristic of the curve, the distance from the saddle point to the trough of the curve is approximate to the distance from the peak to the saddle point of the curve. Accordingly, in the present embodiment, when the slope of the characteristic curve reaches the maximum value of the region, the distance between the current focusing position and the peak position of the characteristic curve is calculated, and then the distance is equal to estimate the valley position of the characteristic curve.
For example, fig. 4A to 4C are exemplary fast focusing methods of image capturing apparatuses according to an embodiment of the present invention. Fig. 4A shows a curve of the focus value FV1 ═ SUM (FV1 × FV1) of the first scale image according to the moving step number in the foregoing embodiment, and fig. 4B shows a curve of the focus value FV2 ═ SUM (FV2 × FV2) of the second scale image according to the moving step number in the foregoing embodiment. Fig. 4C shows a curve of the ratio SFV of the focus value FV2 to the focus value FV1 as FV2/FV 1. As can be seen from the trend of the change of the focus value S1 in fig. 4C, when the number of lens shift steps reaches the bottom of the hill on the left side of the curve FV1 or the curve FV2, the lens shift steps are around the peak P1 of the characteristic curve SFV. When the peak P1 of the characteristic curve SFV is crossed, the slope of the characteristic curve SFV changes from a positive value to a negative value and continuously increases, and when the local maximum value is reached (i.e., after reaching the local maximum value, the slope changes to decrease), it is determined that the current in-focus position reaches the saddle point P2 of the characteristic curve SFV. At this time, based on the symmetrical characteristic of the characteristic curve SFV, the distance from the saddle point P2 to the trough P3 will be approximately the distance d1 from the peak P1 to the saddle point P2. Accordingly, the position of the trough P3 can be estimated by adding the distance d1 to the number of moving steps corresponding to the saddle point P2.
Similarly, when the number of lens shift steps reaches the lower margin of the curve FV1 or the right side of the curve FV2 as seen from the trend of change in the focusing value S2 in fig. 4C, the lens shift step is approximately near the peak P4 of the characteristic curve SFV. When the peak P4 of the characteristic curve SFV is crossed, the slope of the characteristic curve SFV changes from a negative value to a positive value and continuously increases, and when the local maximum value is reached (i.e., after reaching the local maximum value, the slope changes to decrease), it is determined that the current in-focus position reaches the saddle point P5 of the characteristic curve SFV. At this time, based on the symmetrical characteristic of the characteristic curve SFV, the distance from the saddle point P5 to the trough P3 will be approximately the distance d2 from the peak P4 to the saddle point P5. Accordingly, the position of the trough P3 can be estimated by adding the distance d2 to the number of moving steps corresponding to the saddle point P5.
Returning to the flow of fig. 3, the lens control circuit 26 controls the lens 22 to move to the number of moving steps corresponding to the trough, and then to the number of moving steps corresponding to the peak of the first curve or the second curve to complete focusing (step S308). In detail, the lens control circuit 26 controls the lens 22 to move to the moving steps corresponding to the trough at a first speed, and then to move to the moving steps corresponding to the peak of the first curve or the second curve at a second speed, so as to complete the focusing, wherein the second speed is smaller than the first speed. The lens control circuit 26 can control the actuator of the lens 22 to move the lens 22 to the above-mentioned moving steps or move the lens 22 to the above-mentioned moving steps in a gradual manner, and then perform a small step search to observe the change of the first curve or the second curve, and when the maximum value of the first curve or the second curve is reached, the focusing is completed.
By the method, the steps of the second stage and the third stage in the hill climbing mechanism can be omitted or reduced, so that the focusing speed is improved.
In summary, the image capturing apparatus and the fast focusing method thereof of the present invention calculate the contrast values of the images with different scales and analyze the variation trend thereof to estimate the area where the optimal focusing position is located in advance during the focusing process, thereby controlling the lens to move in one step or move asymptotically to the vicinity of the optimal focusing position, and finally performing a small step search to complete the focusing. Therefore, the focusing speed can be improved, and the phenomenon that the shooting experience of a user is influenced due to the fact that the lens moves back and forth to cause image change can be avoided.
Although the present invention has been described with reference to the above embodiments, it should be understood that the invention is not limited to the embodiments, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention.
Claims (12)
1. A fast focusing method of an image capturing device is characterized in that the image capturing device comprises a lens, an image sensor, a lens control circuit and a focusing circuit, and the method comprises the following steps:
controlling the lens to move by the lens control circuit so as to shoot images by the image sensor;
calculating a first curve of a focusing value of the shot image at a first scale relative to the moving steps of the lens and a second curve of the focusing value at a second scale relative to the moving steps of the lens by the focusing circuit;
dividing, by the focus circuit, the focus value of the second curve by the focus value of the first curve to obtain a characteristic curve;
calculating the distance between the peak and the moving step number corresponding to the saddle point according to the positions of the peak and the saddle point appearing in the characteristic curve, and estimating the position of the trough by adding the distance to the moving step number corresponding to the saddle point; and
and the lens control circuit controls the lens to move to the moving step number corresponding to the wave trough and then to the moving step number corresponding to the wave crest of the first curve or the second curve so as to finish focusing.
2. The method of claim 1, wherein the step of calculating, by the focus circuit, the first curve of the focus value of the image captured by the image sensor at the first scale relative to the number of steps of movement of the lens comprises:
calculating a contrast value of a plurality of pixels in the image of the first scale by using an image contrast algorithm; and
calculating the sum of powers of contrast values of the pixels in the image within a focusing frame as the focusing value of the image at the first scale.
3. The method of claim 1, wherein the step of calculating, by the focus circuit, the second curve of the focus value of the image captured by the image sensor at the second scale relative to the number of steps of movement of the lens comprises:
calculating a contrast value of a plurality of pixels in the image of the second scale by using an image contrast algorithm; and
calculating the sum of powers of contrast values of the pixels in the image located within a focusing frame as the focusing value of the image at the second scale.
4. The method of claim 1, wherein the length and width of the second scale are fractions of the length and width of the first scale.
5. The method of claim 1, after obtaining the characteristic curve, further comprising:
calculating the change of the slope of the characteristic curve in the process of shooting the image by moving the lens;
when the slope is changed to zero, judging that the peak of the characteristic curve is reached; and
when the slope changes from zero to a maximum, it is judged that the saddle point of the characteristic curve is reached.
6. The method of claim 1, wherein the step of controlling the lens to move to the moving step number corresponding to the valley and then to the moving step number corresponding to the peak of the first curve or the second curve by the lens control circuit to complete focusing comprises:
controlling the lens to move to the moving step number corresponding to the wave trough at a first speed by the lens control circuit; and
and controlling the lens to move to the moving step number corresponding to the peak of the first curve or the second curve at a second speed by the lens control circuit, wherein the second speed is less than the first speed.
7. An image capture device, comprising:
a lens;
the image sensor is coupled with the lens and is used for shooting images;
the lens control circuit is coupled with the lens and controls the lens to move so as to shoot the image;
a focusing circuit coupled to the image sensor and the lens control circuit for calculating a first curve of a focusing value of the image captured by the image sensor relative to the moving steps of the lens at a first scale and a second curve of the focusing value relative to the moving steps of the lens at a second scale, dividing the focusing value of the second curve by the focusing value of the first curve to obtain a characteristic curve, calculating a distance between a peak and the moving steps corresponding to a saddle point according to positions of the peak and the saddle point appearing in the characteristic curve, and adding the distance to the moving steps corresponding to the saddle point to estimate a position of a valley, wherein the focusing circuit is coupled to the image sensor and the lens control circuit, and the distance is added to the moving steps corresponding to the saddle point forward to estimate the position of the valley
The lens control circuit controls the lens to move to the moving step number corresponding to the wave trough estimated by the focusing circuit and then to move to the moving step number corresponding to the wave crest of the first curve or the second curve to finish focusing.
8. The image capture device of claim 7, wherein the focus circuit comprises using an image contrast algorithm to calculate contrast values for a plurality of pixels in the image at the first scale, and calculating a sum of powers of the contrast values for the pixels in the image that are within a focus frame as the focus value of the image at the first scale.
9. The image capture device of claim 7, wherein the focus circuit comprises using an image contrast algorithm to calculate contrast values for a plurality of pixels in the image at the second scale, and calculating a sum of powers of the contrast values for the pixels in the image that are within a focus frame as the focus value of the image at the second scale.
10. The image capturing device of claim 7, wherein the length and width of the second dimension are fractions of the length and width of the first dimension.
11. The image capturing apparatus as claimed in claim 7, wherein the focus circuit calculates a change in a slope of the characteristic curve during the lens movement to capture the image, wherein the peak of the characteristic curve is determined to be reached when the slope is changed to zero, and the saddle point of the characteristic curve is determined to be reached when the slope is changed from zero to a maximum value.
12. The image capturing device as claimed in claim 7, wherein the lens control circuit controls the lens to move to the moving steps corresponding to the valleys at a first speed, and then controls the lens to move to the moving steps corresponding to the peaks of the first curve or the second curve at a second speed, wherein the second speed is lower than the first speed.
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| JP2004226532A (en) * | 2003-01-21 | 2004-08-12 | Victor Co Of Japan Ltd | Automatic focusing device |
| CN101098407A (en) * | 2006-06-30 | 2008-01-02 | 索尼株式会社 | Auto-focus apparatus, image capture apparatus, and auto-focus method |
| JP2010107578A (en) * | 2008-10-28 | 2010-05-13 | Panasonic Corp | Automatic focusing device |
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| CN104853087A (en) * | 2015-03-16 | 2015-08-19 | 浙江宇视科技有限公司 | Identification and focusing method for point light source scene |
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